Method of improving the viscosity index of lubricating oils

ABSTRACT

1. A METHOD OF IMPROVING THE VI OF AN AROMATIC-CONTAINING LUBRICATING OIL BOILING ABOVE 650*F. WHICH COMPRISES: (A) CONTACTING A RELATIVELY LOW VI AROMATIC-CONTAINING LUBRICATING OIL WITH A BENZENECARBOXYLIC ACID ANHYDRIDE FOR A TIME SUFFICIENT OF FORM A COMPLEX OF SAID ANHYDRIDE WITH LOW VI AROMATIC COMPONENTS OF THE OIL, AND (B) SEPARATING THE COMPLEX FROM THE REMAINING OIL, WHEREBY THERE IS OBTANED A RELATIVELY HIGH VI LUBRICATING OIL.

United States Patent 3,843,513 METHOD OF IMPROVING THE VISCOSITY INDEX OF LUBRICATING OILS Raymond Wynkoop, Gladwyne, Pa., assignor to Sun Ventures, Inc., St. Davids, Pa. No Drawing. Filed Oct. 29, 1973, Ser. No. 410,593 Int. Cl. C10m 11/00 US. Cl. 208282 7 Claims ABSTRACT OF THE DISCLOSURE The VI of lubricating oils is improved by treating them with a benzenecarboxylic acid anhydride such as trimellitic anhydride (herein TMA). The anhydride forms a complex with certain low VI aromatics in the oil and removal of the complex effects an improvement in the VI of the remaining oil.

CROSS REFERENCE TO RELATED APPLICATION Copending application Ser. No. 410,594, filed by myself of even date herewith relates to the use of TMA to effect separation of certain types of alkylnaphthalenes from non-lubricating oil mixtures thereof.

BACKGROUND OF THE INVENTION It is well known that viscosity index (VI) of a lubricating oil is an important quality characteristic and gen erally, the higher the VI the better the oil. This is generally true whether the oil is paraffinic, naphthenic or aromatic.

The characterization of lubricating oils as parafiinic, naphthenic or aromatic is determined by those skilled in the art on the basis of viscosity gravity constant (VGC) and not by whether the chemical components of the oil are paraffinic, naphthenic, etc. Most oils contain all three types of compounds in amounts that overlap considerably between the three types of oils. However, almost all nonsynthetic oils contain significant quantities of aromatics. Parafiinic oils may contain 1035% and naphthenics 15- 50% and aromatic oils sometimes higher than 50%. By accepted definition paraffinic, naphthenic and aromatic lubricating oils have VGCs, respectively, of less than .82, .82-.90 and above .90.

Lubricating oils are distinguished from other types of oil in that they have an SUS viscosity at 100 F. between 40 and 12,000, usually IOU-12,000. Further, lubricating oils generally boil above 650 F.

Since the VI of a lubricating oil is important, numerous means have been discovered to improve the VI. Many of these take the form of additives. Recently hydrocracking has been employed to produce lubes of higher VI than can be achieved with the more traditional solvent extraction processes for lube manufacture.

In preparing hydrocracked lubes a feedstock boiling above 650 F. (e.g. 7001200 F.) such as a topped crude, a distillate from an atmospheric resid, etc. is passed over a catalyst that has both hydrogenation and cracking activity. Typically such a catalyst contains minor amounts of at least two metals of the group nickel, cobalt, molybdenum, and tungsten, the combination serving as the hydrogenation component. They are deposited on a silica-alumina support as this has adequate cracking activity.

Operating conditions are selected so that 1090%, usually 25-75 volume percent of the product (hydrocrackate) boils within the feedstock boiling range, the balance boiling below that. Typical conditions are a temperature of 500l500 F., a liquid hourly space velocity of 0.1 and a hydrogen pressure greater than 1000 p.s.i.a. US. Pat.

Patented Oct. 22, 1974 SUMMARY OF THE INVENTION According to the invention low VI components of aromatic-containing lubricating oils are removed from the oil by treatment with a benzenepolycarboxylic acid anhydride. The anhydride complexes with the low VI components and the complex is thereafter removed as by filtration.

DESCRIPTION OF THE INVENTION The complexing agent is a benzenepolycarboxylic acid anhydride. These materials are well known and are described in Advanced Organic Chemistry, Fieser & Fieser, Reinhold Publishing Company, 1962, pp. 804-807. Suitable materials are the monoand polyanhydrides of the three phthalic acids, hemimellitic acid, trimellitic acid, trimesic acid, mellophanic acid, pyromellitic acid, benzenepentacarboxylic acid, and mellitic acid. Only one anhydride group need be present event though four or more carboxylic acid groups are present. The acid corresponding to the anhydride used in the invention preferably contains at least three carboxylic acid groups, preferably just three, and more preferably is trimellitic acid. The aforesaid Fieser et al. reference describes suitable methods for preparing the anhydrides suitable for the present purpose. In describing the invention hereinafter the anhydride will be assumed to be trimellitic anhydride.

The lubricating oil will normally have at least 10% aromatics (by weight by ASTM clay gel analysis) usually at least 20% and preferably at least 35%. It can be paraflinic naphthenic or aromatic but is preferably naphthenic or aromatic, preferably aromatic. In any case it will have the viscosity and boiling range criteria specified previously. Preferably the lube oil is petroleum derived, i.e., non-synthetic, and preferably it is obtained by a hydrocracking process.

The complexing can be carried out by contacting, that is mixing, the TMA in the lubricating oil. Preferably the contacting is under such conditions, e.g., elevated temperature, that the TMA actually dissolves in the oil but this is not essential. The temperature at which the complexing is carried out will usually be 0-300 C. but this is not critical. The formation of the complex proceeds much faster at elevated temperature so usually a temperature of 25l50 C. will be employed, preferably -150" C.

The complex is believed to contain one mole of aromatic per mole of T MA, but there may be isolated cases where it is not one to one. The amount of TMA employed will vary considerably depending on the complexing agent employed, the aromatic content of the oil, and the like. Normally, however, the TMA will be 150% by weight of the lube oil being treated, usually 5-30%. The amount of TMA used will also usually be one mole or less per mole of aromatic removed.

If the complexing is carried out at elevated temperature the entire mass is then cooled to effect precipitation of the complex. Cooling to or somewhat above room temperature is usually adequate and cooling too far below this is disadvantageous since uncomplexed material will ultimately also precipitate. Cooling the mass to room temperature is advantageous not only because it effects additional complex precipitation but also because the solubility of TMA in the oil at room temperature is much lower. It should be noted that some precipitation of the complex will usually occur at the temperature at which the TMA and lubricating oil is mixed. For example if a lube oil is mixed with TMA at C. a precipitate of complex quickly forms and cooling the mass to room temperature effects further complex precipitation.

After separating the precipitated complex the remaining oil has a higher VI than the original oil without sig nificant change in other properties such as viscosity.

The separated complex can be decomposed to recover the TMA and, if desired, the individual aromatics removed from the oil. The specific aromatics will vary from oil to oil but they are all relatively low VI aromatics in the sense that their removal effects a VI increase in the remaining oil. The specific aromatics can be determined by analysis (e.g., chromatography) and subsequent complex obtained can be decomposed by heating to their boiling points. They can all be distilled off together and later fractionated into components or they can be recovered separately from the complex itself by heating the complex to the boiling points of the aromatic components thereof, beginning with the lowest boiling component.

Another method of effecting complex decomposition is by aqueous extraction. For example the complex is contacted with a hot (e.g. 70 C.) dilute (2.5 weight percent) solution of trimellitic acid. The anhydride portion of the complex dissolves in the aqueous acid solution leaving a supernatant layer of the hydrocarbon components of the complex. The hydrocarbon layer is decanted and then distilled separate the various components thereof.

Another method of carrying out the contacting is in a countercurrent extraction column which column can be a single column or a plurality of separate zones. In this technique lubricating oil enters at, say, the bottom of the column and TMA at the top. The TMA and. oil flow countercurreutly to each other with the complex forming as the TMA" passes down the column. The TMA is removed from the bottom of the column as complex and treated oil is removed from the top of the column.

The following example illustrates my invention more specifically.

EXAMPLE Viscosity Viscosity index (ESL/100 F. (Est/210 F.

Untreated 83. 13. 6 3. 0 Treated 89. 2 l3. 2 3. 0

It is apparent from the above that a significant VI improvement has been achieved without any significant change in the oil viscosity. Similar results are achieved with other benzenepolycarboxylic acid anhydrides and other types of lube oils. The actual VI improvement will vary from oil to oil but will almost always be at least 5 units usually 10-15.

The invention claimed is:

1. Method of improving the VI of an aromatic-containing lubricating oil boiling above 650 F. which comprises:

(a) contacting a relatively low VI aromatic-containing lubricating oil with a benzenecarboxylic acid anhydride for a time sufiicient to form a complex of said anhydride with low VI aromatic components of the oil, and

(b) separating the complex from the remaining oil,

whereby there is obtained a relatively high VI lubrieating oil.

2. Method according to Claim 1 wherein said anhydride is trimellitic anhydride.

3. Method according to Claim 1 wherein in Step (a) the anhydride is dissolved in the oil at a temperature above 25 C. and the resulting solution is, in Step (b), cooled to crystallize the complex.

4. Method according to Claim 1 wherein said lubricating oil has a viscosity gravity constant above 0.90.

5. Method according to Claim 1 wherein said lubricating oil in Step (a) contains at least 20% aromatics.

6. Method according to Claim 1 wherein the amount of said anhydride in Step (a) is 530% by weight of said lubricating oil.

7. Method according to Claim 1 wherein said relatively low VI lubricating oil has a viscosity at F. of 40- 12,000 SUS, boils above 650 F. and is obtained by contacting a petroleum fraction with a hydrocracking catalyst containing a hydrogenating component deposited on a support having cracking activity, the contacting being carried out above 500 F. and above 1000 p.s.i.a. H pressure such that 25-75 volume percent of the hydrocrackate boils within the boiling range of said petroleum fraction with the balance boiling below such range.

References Cited UNITED STATES PATENTS 3,023,160 2/1962 Stedman 208240 2,927,077 3/ 1960 Jezl 208282 2,002,902 5/1935 Martin et a1. 208256 3,790,472 2/ 1974 White 208-98 3,663,427 5/1972 Thomas et al 20887 DELBERT E. GANTZ, Primary Examiner J. M. NELSON, Assistant Examiner U.S. Cl. X.R. 20818, 87, 96 

1. A METHOD OF IMPROVING THE VI OF AN AROMATIC-CONTAINING LUBRICATING OIL BOILING ABOVE 650*F. WHICH COMPRISES: (A) CONTACTING A RELATIVELY LOW VI AROMATIC-CONTAINING LUBRICATING OIL WITH A BENZENECARBOXYLIC ACID ANHYDRIDE FOR A TIME SUFFICIENT OF FORM A COMPLEX OF SAID ANHYDRIDE WITH LOW VI AROMATIC COMPONENTS OF THE OIL, AND (B) SEPARATING THE COMPLEX FROM THE REMAINING OIL, WHEREBY THERE IS OBTANED A RELATIVELY HIGH VI LUBRICATING OIL. 